Q. 66

# Calculate the pH

(a) for 10 mL of 0.2M Ca(OH)2 and 25 mL of 0.1M HCl

10 ml of 0.2 M Ca(OH)2= 10× 0.2 milimole = 2 milimoles

25 ml of 0.1 M HCl = 25× 0.1 milimole = 2.5 milimoles

Ca(OH)2 + 2HCl ↔ CaCl2 + 2H2O

0.1 a mole of Ca(OH)2 reacts with 2 millimole of HCl

∴ 2.5 mole of HCl reacts with 1.25 millimole of Ca(OH)2

Ca(OH)2 left = 1=1.25 = 0.75 milimole

Volume of reaction mixture = 10mL+ 25mL = 35mL

∴ Molarity of Ca(OH)2in the mixture solution is:

Molarity =

Hence,

Molarity = = 0.0214 M

⇒[OH-] = 2 × 0.0124 M

⇒[OH-] = 0.0428 M

To caculate pOH, we use the formula:

pH = - log[OH-]

⇒pH= - log (4.28× 10-2)

⇒pH = -log 4.28 + 2log 10

⇒pH = 2 – 0.6314

⇒pH = 1.37

As we know that, pH + pOH =14

∴ pH = 14 – 1.37

⇒pH = 12.63

Hence, the pH is 12.62

(b) for 10 mL of 0.01M H2SO4 and 10 mL of 0.01M Ca(OH)2

10 ml of 0.01 M H2sO4 = 10× 0.01 milimole = 0.1 milimole

10 ml of 0.01 M Ca(OH)2 = 10× 0.01 milimole = 0.1 milimole

Ca(OH)2 + H2sO4 = CaSO4 + 2H2O

1 mole of Ca(OH)2 reacts with 1 mole of H2sO4

∴ 0.1 millimole of Ca(OH)2 will react completely with 0.1 minimal of H2SO4. Hence solution will be neutral with pH= 7

(C) 10 mL of 0.1M H2SO4 and 10 mL of 0.1M KOH

10 ml of 0.01 M H2sO4 = 10× 0.01 milimole = 0.1 milimole

10 ml of 0.1 M KOH = 10× 0.1 milimole = 1 milimole

2KOH+ H2sO4 = K2SO4 + 2H2O

I mole of KOHreacts with 0.5 milimole of H2sO4

H2SO4 left = 1=0.5 = 0.5 milimole

Volume of reaction mixture = 10+ 10 = 20 mL

∴ Molarity of H2SO4 in the mixture solution is:

Molarity =

Hence,

Molarity = = 2.5 × 10-12 M

⇒[H+] = 2 × 2.5 × 10-12

⇒[H+] = 5× 10-2

To caculate pH, we use the formula:

pH = - log[H+]

⇒pH= - log (5× 10-2)

⇒pH = -log 5 + 2log 10

⇒pH = 2 – 0.699

⇒pH = 1.3

Hence, the pH is 1.3

Rate this question :

How useful is this solution?
We strive to provide quality solutions. Please rate us to serve you better.
Try our Mini CourseMaster Important Topics in 7 DaysLearn from IITians, NITians, Doctors & Academic Experts
Dedicated counsellor for each student
24X7 Doubt Resolution
Daily Report Card
Detailed Performance Evaluation
view all courses
RELATED QUESTIONS :

Calculate the pH NCERT - Chemistry Part-I

The ionization coNCERT - Chemistry Part-I

Ionic product of NCERT - Chemistry Part-I

Predict if the soNCERT - Chemistry Part-I